A typical gas turbine engine includes a compressor section, a combustion section and a turbine section. The compressor section provides a compressed air flow to the combustion section where the air is mixed with a fuel, such as natural gas, and ignited to create a hot working gas. The working gas expands through the turbine section where it is directed across rows of blades therein by associated vanes. As the working gas passes through the turbine section, it causes the blades to rotate, which in turn causes a shaft to rotate, thereby providing mechanical work.
A turbine component such as an airfoil is exposed to harsh conditions during normal operation of the turbine. As a result, the airfoil may become worn or damaged and may exhibit erosion, mechanical fatigue, cracks, creep and other undesirable conditions. The existence of such wear or damage is undesirable since it frequently compromises operation of the gas turbine. An airfoil typically extends from a platform having a root portion that is attached a portion of the turbine. The airfoil and platform are fabricated by a casting technique as a one-piece part or structure, i.e. a one-piece part or structure that is integrally or unistructurally formed. Therefore, replacement of the airfoil itself while maintaining the platform portion is difficult.
It is desirable to use magnetically impelled arc butt (“MIAB”) welding to install a replacement airfoil. MIAB welding is a forge welding technique that provides a solid-state weld. In MIAB welding, a magnetic field causes movement of an electric arc along respective mating surfaces of first and second components that are to be welded. This uniformly heats the mating surfaces until sufficient plastic deformation occurs to enable forging of the respective mating surfaces. The first and second components are then rapidly brought together under pressure to create a forging action that forms a joint between the first and second components. However, it is difficult to use current MIAB welding techniques to weld components having complex curvatures such as turbine airfoils.